Through constructions that are now
standard [1]}, [2]}, [3]},
the time-dependent solution to Eq. (REF ), converted
to complex arguments by Eq. (REF ), may be written as
the 2-field functional integral
\({\phi }_T \! \left( z \right) =\int _0^T\mathcal {D} {\xi }^{\dagger }\mathcal {D} {\xi }e^{\left( z - {{\xi }^{\dagger }}_T \right) {\xi }_T}e^{- S}{\phi }_0 \!\left({\xi }_0^{\dagger }\right) .\) 
